For example, in a semiconductor manufacturing apparatus, a pressure within a chamber is measured by using a vacuum gauge, and it is, however, known that performance of an ionization vacuum gauge is deteriorated when used in a contaminated environment.
Supposing that the ionization vacuum gauge does not indicate a normal value due to the deterioration, it follows that a large quantity of defective products are produced due to a progress of a semiconductor process under an abnormal condition. At this time, especially in the case of a fault mode in which the value displayed on the ionization vacuum gauge slightly deviates from the normal value, there arises a problem of not being aware of a fault in many cases.
Therefore, a determination of the deterioration has been tried to be made by some methods. Herein, there has hitherto been generally adopted a method of checking soundness of the vacuum gauge by calibrating the vacuum gauge through a test or an examination after removing the vacuum gauge from the semiconductor manufacturing apparatus, and this method has, however, a problem that an operating ratio of the semiconductor manufacturing apparatus drops down because of requiring a considerable length of time and a considerable cost.
A method of making the calibration by introducing a testing gas into a vacuum apparatus does not spread due to an anxiety for contaminating the vacuum apparatus, and due to involving a labor and a cost as well.
Under such circumstances, Patent Document 1 discloses a method of comparing values outputted from two independent vacuum degree detection units based on a same type of principle, and detecting abnormality of the vacuum gauge when a difference therebetween becomes larger than a preset value.